Which tool is commonly used to scan for open ports on a network?

The tool commonly used to scan for open ports on a network is indeed a port scanner. A port scanner operates by sending packets to specific ports on a target machine and analyzing the responses received. This process helps in identifying which ports are open, closed, or filtered. Open ports indicate that there is an application or service listening, while closed ports suggest that the service is not running, and filtered ports signify that a firewall or similar security measure is blocking the scanning attempt.

Port scanning is a crucial part of network security assessment and helps in understanding the network's exposure to potential attacks by revealing available services that could be targeted by attackers. By knowing what ports are open, network administrators can better secure their systems and take necessary actions to mitigate risks.

The other choices represent different tools that serve distinct purposes in network management and security. Packet sniffers capture and analyze the data packets traveling through a network but do not specifically focus on port scanning. Network analyzers provide a broader analysis of network performance and traffic but also do not conduct port scanning specifically. Firewalls are security devices that monitor and control incoming and outgoing network traffic based on predetermined security rules; they don't scan for open ports but often make decisions based on the results of scans.